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This week, at the Conservative Political Action Conference (CPAC) in Washington, D.C., some of the Republican Party's top potential presidential candidates will test their rhetorical skills -- and possible future platforms -- before some of the nation's most dedicated conservatives. But while the high-profile convention could be a great showcase for politicians like Sen. Rand Paul, R-Ky., and Sen. Marco Rubio, R-Fla., there are a few notable omissions from the lineup. Here's a look at who's on the roster - in order of appearance - and who won't be showing up.

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Sen. Marco Rubio, R-Fla.

Sen. Marco Rubio, R-Fla., is considered a rising star in the Republican Party -- and a likely contender for the GOP presidential nomination in 2016. The young, savvy, and Cuban-American senator recently attempted to burnish his foreign policy credentials on a trip to Israel, where he met with Israeli Prime Minister Benjamin Netanyahu, pictured here.

Credit: Office of Sen. Marco Rubio, R-Fla.

Sen. Marco Rubio, R-Fla.

In a speech at CPAC this week, Rubio will continue to lay the groundwork for a possible future candidacy, alongside some of his likely future competitors.

Credit: AP Photo/Charlie Neibergall

Sen. Rand Paul, R-Ky.

Sen. Rand Paul, R-Ky., got a big profile boost last week when his 13-hour spoken filibuster, of the Obama administration's drone program, garnered the widespread attention of conservatives across the country.

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Since then, Paul has said he's "seriously" considering a bid in 2016, and CPAC represents an opportunity for the Kentucky senator to appeal to his party's most fervent conservatives. Libertarians have also made a strong showing at CPAC in the past, often in support of Paul's father, former Republican presidential candidate Ron Paul, R-Tex.

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Gov. Rick Perry, R-Texas

Texas Governor Rick Perry, another prominent CPAC speaker this year, may not have lived up to the hype surrounding his 2012 presidential candidacy, but he's signaled he may throw his hat in the ring for the 2016 competition.

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Gov. Rick Perry, R-Texas

If he does go after the GOP nomination, Perry should have had plenty of time to recover from his infamous "oops" moment during the Republican primary contest, when he froze up while making a point during a GOP debate.

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Rep. Paul Ryan, R-Wis.

Rep. Paul Ryan, R-Wis., recently unveiled his controversial budget proposal on behalf of House Republicans. The plan -- which would balance the budget over the next ten years -- will be a breath of fresh air to fiscal conservatives who favor austerity measures. Expect a lot of those conservatives to be at CPAC.

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Rep. Paul Ryan, R-Wis.

The Wisconsin representative may have fallen short of the vice presidency in 2012, but his run gave the once-little known House Budget Committee chairman national name recognition. And he certainly seems open to leveraging it in a run for the Oval Office four years from now. Shortly after his November loss, the New York Times quoted an aide saying Ryan was "invigorated" by the race.

Credit: AP Photo/Charles Dharapak

Fmr. Sen. Rick Santorum, R-Pa.

Former Sen. Rick Santorum also launched an unsuccessful bid in 2012 -- for the Republican presidential nomination, which he lost to Mitt Romney.

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Fmr. Sen. Rick Santorum, R-Pa.

Santorum, a staunch social conservative, may use his remarks at CPAC to test the waters for another bid.

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Gov. Bobby Jindal, R-La.

Louisiana governor Bobby Jindal is another rising star in the Republican Party, and he, too, will take the stage at CPAC this week.

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Gov. Bobby Jindal, R-La.

Jindal has built a reputation for competence while maintaining a solidly conservative record during his tenure in office. He has already positioned himself as a candidate to take the GOP into the future without abandoning its longstanding positions, distancing himself from Romney's claims that Mr. Obama won reelection by giving "gifts" to key constituencies and arguing that "If we want people to like us, we have to like them first."

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Fmr. Gov. Jeb Bush, R-Fla.

The former Florida governor is a member of one of America's most prominent political dynasties: Both his brother, George W. Bush, and his father, George H.W. Bush, have been recent Republican presidents. Bush has signaled that he, too, is open to the possibility of a bid.

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Fmr. Gov. Jeb Bush, R-Fla.

The Spanish-speaking Republican has close ties to the Latino community, and has long pushed a more liberal approach to immigration reform within his party. But a recent flip-flop on immigration has some to question his motives.

Credit: Mark Wilson

Fmr. Gov. Sarah Palin, R-Alaska

Fmr. Gov. Sarah Palin, R-Alaska, isn't considered a serious presidential contender these days, but she can still attract quite a crowd at conservative events like CPAC, where she'll appear yet again this year.

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Fmr. Gov. Sarah Palin, R-Alaska

Whether or not she'll seek future political office, however, remains to be seen: Most recently, she announced she'll be writing a book about Christmas.

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Gov. Nikki Haley, R-S.C.

Nikki Haley, South Carolina's Indian-American governor, is an unflinching conservative with Tea Party support. She also happens to be a woman and a minority - a combination that has helped her rise to national prominence since she won the governorship in 2010.

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Gov. Nikki Haley, R-S.C.

But Haley, who has been known be a divisive figure even within her party, turned down her invitation to speak at the convention.

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Gov. Chris Christie, R-N.J.

New Jersey Governor Chris Christie is another major contender for the nomination in 2016. The brash, charismatic figure reportedly turned down repeated pleas to run in 2012, and he was the keynote speaker at last year's Republican National Convention.

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Gov. Chris Christie, R-N.J.

But the governor's tendency to work with Democrats -- including President Obama -- hasn't sat so well with everyone. Christie was pointedly not invited to speak at CPAC this year -- a fact that didn't seem to bother him too much.

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Gov. Bob McDonnell, R-Va.

Republican Gov. Bob McDonnell, of Virginia, was thought to be on Romney's vice presidential short list, and he made a handful of appearances with the GOP nominee on the trail.

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Gov. Bob McDonnell, R-Va.

But he, too, was left of the CPAC invite list -- possibly because he recently backed a transportation bill that raises taxes in Virginia.